Diselenide-containing poly(ε-caprolactone)-based thermo-responsive hydrogels with oxidation and reduction-triggered degradation

Herein, novel multi-responsive injectable polyester hydrogels were reported based on the diselenide-containing poly(ε-caprolactone) copolymers ((mPEG-PCL-Se)₂). The (mPEG-PCL-Se)₂ solution remained a free-flowing state at ambient temperature but spontaneously turned into a semisolid hydrogel upon heating to physiologic temperature. The phase transition temperature was examined to be dependent on the composition and aqueous concentration of the copolymers. More importantly, the thermo-responsive hydrogels were endowed with oxidation and reduction-triggered degradation by the incorporation of diselenide groups. Accordingly, the degradation of poly(ε-caprolactone)-based hydrogels was greatly improved and the rate of degradation was well regulated by the concentration of hydrogen peroxide (H₂O₂) or glutathione (GSH). This superior stimuli-responsive degradation could lead to an enhanced drug release of encapsulated drug (Doxorubicin, DOX). Thus the oxidation and reduction-triggered degradable diselenide-containing poly(ε-caprolactone) hydrogels would offer great potential for the controlled drug delivery.     

Synthesis and biodegradation of poly(2-pyrrolidone-co-ε-caprolactone)s

Copolyesteramides of 2-pyrrolidone with ε-caprolactone were synthesized by ring-opening copolymerization. The copolymers were random-like and their melting temperature and heat of fusion were dependent on the polymer composition. Biodegradation by a polyamide 4 (PA4) degrading microorganism showed rapid degradation in the region of amide-rich polymer composition. On the contrary, enzymatic hydrolysis using a lipase resulted in a different tendency, that is, ester-rich copolymers hydrolyzed rapidly. Activated sludge makes copolymers degrade to CO₂ in wide polymer composition ratio. Copolyesteramides are expected to be applied as an environmentally-friendly plastics or bioabsorbable polymers in medical fields.     

A facile synthesis of per (poly )fluoroalkyl substituted α-amino acid derivatives

Initiated by CrCl3/Fe redox couple, per(poly)fluoroalkyl iodides added to methyl a-acetylamino acrylate, giving B-per(poly)fluoroalkyl a-amino acid derivatives in good yields.     

High temperature pyrolysis of poly(phenylene vinylene)s with poly(ε-caprolactone) or polystyrene side chains

Journal of Thermal Analysis and Calorimetry - High temperature pyrolysis studies of poly(phenylene vinylene)s PPVs with lateral substituents poly(ε-caprolactone) (PPV–PCL) or...     

Melting of poly(ε-caprolactone) studied by step-heating calorimetry

This study demonstrates that the step-heating calorimetry, which is a kind of temperature-modulated differential scanning calorimetry, can provide valuable information on the polymer melting. Time-dependent heat flow due to the melting of lamellar crystallites in a narrow range of thickness can be directly observed, from which thickness distribution of lamellar crystallites and thickness dependence of the melting kinetics are deduced. A sample of poly(ε-caprolactone) was used as a model material of semi-crystalline polymer, which has high crystallinity (0.79) so that no recrystallization and/or reorganization occur during melting in the step-heating scan. It was revealed that superheating dependence of the melting rate coefficient increases with increasing lamellar thickness, which may be attributed to variation of the fold surface roughness with respect to lamellar thickness. Analysis based on the cylindrical nucleation model revealed much lower free energy values of lateral surface than that evaluated from crystallization behavior, suggesting that the nucleus for melting is more stable than that for crystallization.     

Development of orientation during electrospinning of fibres of poly(ε-caprolactone)

We explore the influence of a rotating collector on the internal structure of poly(ε-caprolactone) fibres electrospun from a solution in dichloroethane. We find that above a threshold collector speed, the mean fibre diameter reduces as the speed increases and the fibres are further extended. Small-angle and wide-angle X-ray scattering techniques show a preferred orientation of the lamellar crystals normal to the fibre axis which increases with collector speed to a maximum and then reduces. We have separated out the processes of fibre alignment on the collector and the orientation of crystals within the fibres. There are several stages to this behaviour which correspond to the situations (a) where the collector speed is slower than the fibre spinning rate, (b) the fibre is mechanically extended by the rotating collector and (c) where the deformation leads to fibre fracture. The mechanical deformation leads to a development of preferred orientation with extension which is similar to the prediction of the pseudo-affine deformation model and suggests that the deformation takes place during the spinning process after the crystals have formed.     

Controlled-release and antibacterial studies of doxycycline-loaded poly(ε-caprolactone) microspheres

The objective of the present study is to achieve doxycycline’s maximum therapeutic efficacy. Doxycycline-loaded poly(ε-caprolactone) microspheres were prepared by water-in-oil-in-water (w/o/w) double emulsion solvent evaporation technique with different formulation variables such as concentrations of drug and polymer. The effects of these variables on surface morphology, particle size distribution, encapsulation efficiency, and in vitro release behavior were examined. To observe the nature of microspheres, X-ray diffraction studies were carried out. The release data obtained were determined using various kinetic models and Korsmeyer–Peppas model showed an acceptable regression value for all compositions. Antibacterial efficiency of doxycycline-loaded poly(ε-caprolactone) microspheres were assessed by determining Minimum Inhibition Concentration (MIC) by standard tube dilution method against four standard pathogenic strains. The in vitro drug release studies were carried out in phosphate buffer solution (pH 7.2). The results showed marked retardation of doxycycline release and higher percentage of polymer gave longer drug release profile. This may definitely provide a useful controlled-release drug therapy and also prove to be effective over a long period of time (76 h).     

Effect of ethanol solution of iodine on degradation of poly(ε-caprolactone)

The study of the effect of iodine on the degradation of poly(ε-caprolactone) fibers has revealed a drastic decrease in their molecular weight upon 24 h exposure to a 10% iodine solution in ethanol. It has been assumed that the main mechanism of this degradation is alcoholysis which proceeds with an efficient rate constant of nearly 7.5 × 10^–3 h^–1     

Viscoelastic behaviors of poly(ε-caprolactone)/attapulgite nanocomposites

Nanocomposites based on biodegradable poly(ε-caprolactone) (PCL) and attapulgite (AT) were prepared by solution blend. The morphology and rheological behaviors of the blends were examined. SEM observation showed that AT nano-rods were well dispersed in the PCL matrix in a nanometer scale at low AT content and a severe aggregation would happen at high AT content. The rheological behaviors of the polymer/fibrous clay nanocomposite samples were investigated by an Advanced Rheometric Expansion System with parallel plate geometry. The effects of AT content on the viscoelastic behaviors of the PCL/AT nanocomposites were also confirmed by rheological analysis. The apparent activation energies of flow were calculated by the Arrhenius equation.     

In-chain functionalized poly(ε-caprolactone): A valuable precursor towards the synthesis of 3-miktoarm star containing hyperbranched polyethylene

Well-defined 3-miktoarm star copolymer 3μ-HBPE(PCL)₂ (HBPE: hyperbranched polyethylene, PCL: poly[ε-caprolactone]) was synthesized by combining chain walking polymerization (CWP), ring-opening polymerization (ROP), and “click” chemistry. The synthetic methodology includes the following steps: (a) synthesis of in-chain ethynyl-functionalized PCL, (PCL)₂-C ≡ CH by ROP of ε-caprolactone (CL) with ethylene-functionalized solketal (3-[prop-2-yn-1-yloxy] propane-1,2-diol) as difunctional initiator and phosphazene superbase t-BuP₂ as catalyst; (b) synthesis of azido-functionalized hyperbranched PE (HBPE-N₃) by CWP of ethylene with α-diimine-Pd(II) catalyst, followed by quenching with excess 4-vinylbenzyl chloride and transformation of chloro to azide group with sodium azide; and (c) “clicking” HBPE-N₃ and (PCL)₂-C ≡ CH using copper(I)-catalyzed azide–alkyne cycloaddition. ¹H NMR spectroscopy, gel permeation chromatography, Fourier-transform infrared spectroscopy, and differential scanning calorimetry were used to determine the molecular characteristics and thermal properties of the polymers. Self-assembly behavior of 3μ-HBPE (PCL)₂ in petroleum ether, a selective solvent for HBPE, was investigated by dynamic light scattering, atomic force microscopy, and transmission electron microscopy. The in-chain alkyne-functionalized poly(ε-caprolactone) is a valuable precursor for PCL-based complex macromolecular architectures.     

Thermal,mechanical, and topographical evaluation of nonstoichiometric α-cyclodextrin/poly(ε-caprolactone) pseudorotaxane nucleated poly(ε-caprolactone) composite films

Three pseudorotaxanes (PpR) comprised of poly (ε-caprolactone) (PCL) and α-cyclodextrin (α-CD) with varying stoichiometric ratios were synthesized and characterized. Wide-angle X-ray diffraction (WAXD) and thermogravimetric (TGA) analyses provided conclusive evidence for complexation between the guest PCL and host α-CD. The as-synthesized and characterized PpRs were used at 10 and 20% concentrations as nucleants to promote the bulk PCL crystallization in composite films. Both WAXD and TGA provided evidence for intact PpR structures in the composite films. Isothermal differential scanning calorimetric (I-DSC) analyses, performed at various crystallization temperatures demonstrated significant differences in the crystallization patterns among the composite films. In addition, I-DSC analyses showed higher Avrami constant values (n) in the PpR-nucleated composite PCL films (n ~ 3), indicating 3-dimensional crystal growth. In the case of neat PCL films, however, lower n values indicated crystal growth in 1-dimensions or 2-dimensions. Moreover, atomic force microscopic analyses showed large crests and pits in PpR-nucleated PCL composites, with irregular morphologies leading to higher surface roughness. To the contrary, the crests and pits were much smaller in the neat PCL films, resulting in lower surface roughness values. Finally, mechanical testing revealed higher tensile strength for PpR-nucleated PCL composites films, demonstrating larger load bearing capabilities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1529–1537     

Novel electrospun poly(ε-caprolactone)-based bicomponent nanofibers possessing surface enriched in tertiary amino groups

For the first time preparation of electrospun poly(ε-caprolactone) (PCL) based nanofibers possessing surface enriched in tertiary amino groups is shown. For that purpose the pair PCL and poly(ε-caprolactone)-b-poly[(2-dimethylamino)ethyl methacrylate] (PCL-b-PDMAEMA) diblock copolymers was used. PCL-b-PDMAEMA copolymers were synthesized using a combination of ring-opening polymerization and atom transfer radical polymerization (ATRP). Nanofibers with mean diameters ranging from 400 to 800 nm were obtained. Their morphology was evaluated by scanning electron (SEM) and atomic force microscopy (AFM). It was found that the morphology of the fibers depended on the weight ratio between the partners and the length of the PDMAEMA-block in the copolymers. The enrichment of the fiber surface in tertiary amino groups was studied by X-ray photoelectron spectroscopy (XPS). Increasing the copolymer content and the length of the PDMAEMA-block led to increase of the amount of tertiary amino groups on the fiber surface. The AFM analyses of the mechanical properties of the fiber surface showed that increasing the copolymer content led to decrease of the surface stiffness. The increase of the copolymer content led also to decrease of the melting temperature and the crystallinity degree in respect to PCL from the (co)polymer as determined by differential scanning calorimetry.     

Enhanced photodegradation of TiO2-containing poly(ε-caprolactone)/poly(lactic acid) blends

The calamitous accumulation of plastic waste in the environment, especially single-use disposables, calls for new approaches to materials design. One method to address the persistence of plastics beyond their intended use is to impart them with functionalities that will either allow for their recyclability or their degradation to basic natural components. This work focuses on the fabrication of photodegradable polyester blends and investigates the impact of compatibilization on photodegradation rates. Specifically, we blended poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) polymers by (reactive) extrusion in the presence or absence of dicumyl peroxide (DCP), a radical generator, and titanium dioxide (TiO₂), an inorganic photocatalyst. We examined the effects of DCP and TiO₂ loadings as well as copolymer composition on the thermomechanical properties, photodegradability, and morphology. We found that the inclusion of TiO₂ dramatically increased flexural moduli and photodegradation rates in both dry and wet conditions, while reactive compatibilization had little effect of the tested properties. This simple and scalable approach is promising to fabricate materials that can readily photodegrade.     

Synthesis and properties of poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) copolyesters

Bio-based poly(isosorbide 2,5-furandicarboxylate-co-ε-caprolactone) (PIFCL) copolyesters were synthesized from 2,5-furandicarboxylic acid, isosorbide and ε-caprolactone. The obtained copolyesters were characterized by ¹H NMR, ¹³C NMR, intrinsic viscosity, GPC, DSC, TGA and tensile testing. The NMR characterization results confirmed the insertion of lactones units into poly(isosorbide 2,5-furandicarboxylate) (PIF) chains. All PIFCL copolyesters were amorphous with T_{D, 5%} higher than 300 °C. The glass transition temperatures of PIFCLs with FDCA molar ratio from 74% to 45% were within the range of 132.1 °C and 72.4 °C. Tensile testing revealed that introduction of ε-caprolactone into PIF chain imparted PIFCL with excellent mechanical performance, typically, PIFCL polyseter with FDCA molar ratio of 45% had a Young's modulus 858 ± 92 MPa, a tensile strength 44 ± 4 MPa and an elongation at break 480 ± 45%.     

Design of cross-linked semicrystalline poly(ε-caprolactone)-based networks with one-way and two-way shape-memory properties through Diels-Alder reactions

Cross‐linked poly(ε‐caprolactone) (PCL)‐based polyesterurethane (PUR) systems have been synthesized through Diels–Alder reactions by reactive extrusion. The Diels–Alder and retro‐Diels–Alder reactions proved to be useful for enhancing the molecular motion of PCL‐based systems, and therefore their crystallization ability, in the design of cross‐linked semicrystalline polymers with one‐way and two‐way shape‐memory properties. Successive reactions between α,ω‐diol PCL (PCL₂), furfuryl alcohol, and methylene diphenyl 4,4′‐diisocyanate straightforwardly afforded the α,ω‐furfuryl PCL‐based PUR systems, and subsequent Diels–Alder reactions with N,N‐phenylenedimaleimide afforded the thermoreversible cycloadducts. The cross‐linking density could be modulated by partially replacing PCL‐diol with PCL‐tetraol. Interestingly, the resulting PUR systems proved to be semicrystalline cross‐linked polymers, the melting temperature of which (close to 45 °C) represented the switching temperature for their shape‐memory properties. Qualitative and quantitative measurements demonstrated that these PUR systems exhibited one‐way and two‐way shape‐memory properties depending on their cross‐linking density.     

Hydrophobicities of poly(ε-caprolactone) oligomers functionalized with different succinic anhydrides

Different succinic anhydrides were used for modification of hydrophobicities of linear and star-shaped poly (ε-caprolactone) oligomers with different molecular weights. Hydroxyl-terminated poly(ε-caprolactone) oligomers were acid-functionalized either with succinic anhydride (SAH) or with alkenylsuccinic anhydrides (ASAs) containing 8 or 18 carbons in their alkenyl chains. Hydrophobicities of the linear and corresponding star-shaped oligomers were investigated by immersion studies and by water contact angle measurements. In comparison with SAH functionalized oligomers, alkenyl chain containing oligomers showed lower thermal transitions and higher hydrophobicities. In addition, oligomers with 18 carbons alkenyl chain showed considerably higher hydrophobicities than corresponding oligomers with 8 carbon alkenyl chain.     

Anionically prepared poly(ε-caprolactam-co-ε-caprolactone) and poly(ε-caprolactam-co-δ-valerolactone) copolymers: Thermal and mechanical properties

Thermal and representative physico-mechanical properties of newly prepared poly[(ε-caprolactam)-co-(ε-caprolactone)] and poly[(ε-caprolactam)-co-(δ-valerolactone)] copolymers were studied. The copolymers were synthesized by anionic polymerization of ε-caprolactam activated by isocyanate end-capped oligomeric aliphatic polyesters designated as the macroactivators (MAs). Type, concentration and molecular weight of the MAs were varied, which resulted in copolymers with different structure and properties. The impact of the new MAs used in this study on the glass transition temperature and the melting temperature of poly-ε-caprolactam was investigated by DSC. DMTA was used to analyze the effect of copolymerization on the storage modulus (E^′) and tan δ of poly-ε-caprolactam. Conventional and high-resolution TGA data revealed that all the synthesized polyesteramides possess good thermal stability. Mechanical properties were studied by notched impact and tensile testing. According to the experimental data the impact toughness increase with the MA content, being six time higher compared to the poly(ε-caprolactam) in the best situation. Water absorption was also considered in relation to the composition of the copolymers.     

Thermomechanical properties of cured isophtalic polyester resin modified with poly(ε-caprolactone)

The effect of a low profile additive, poly(ε-caprolactone) (PCL), on the thermal and mechanical properties of unsaturated polyester resins (UP) was investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and tensile tests. The morphology of the systems has been studied by scanning electronic microscopy (SEM). Two PCL molecular mass were selected (PCL2: M _n = 2000 g mol⁻¹ and PCL50: M _n = 50000 g mol⁻¹) to analyze the influence of the molecular mass and the content of PCL on the UP resins and to establish the relation between thermomechanical behavior and morphology. DSC and DMTA glass transition temperatures (T _g) of the UP cured samples containing PCL indicate that PCL2 is miscible with UP whereas for UP + PCL50 system, T _g values are very close to the ones corresponding to neat UP. Besides in UP + PCL2 systems, one phase morphology is observed in which PCL2 would act as solvent of the reacting mixture along curing process; however, UP + PCL50 systems present phase-separated morphology. The presence of PCL2 and PCL50 in UP resin leads to a decrease of the tensile strength and the Young′s modulus as much notorious as the PCL concentration increases. For UP + PCL2 system the elongation at fracture increases in relation to neat UP, increasing as well with the PCL content.